Wafer handling system with Bernoulli pick-up

ABSTRACT

Wafer handling apparatus operating under the Bernoulli principle to pick up, transport and deposit wafers, which apparatus includes a plate having a plurality of laterally oriented outlets and a central outlet for discharging gas in a pattern sufficient to develop a low pressure enviroment to pick up the wafer while bathing the wafer in radially outflowing gases to prevent intrusion and deposition on the wafer of particulate matter in suspension.

REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of a patent applicationentitled "WAFER HANDLING SYSTEM WITH BERNOULLI PICK-UP", assigned Ser.No. 048,630 and filed on May 11, 1987 now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to wafer handling apparatus for use in asemiconductor processing system and, more particularly, to a pick upwand for lifting wafers without contact with the top or bottom surfacesof the wafer.

2. Description of the Prior Art

Many different types of semiconductor processing systems require the useof wafer handling systems or wafer transport mechanisms. The more widelyused processing systems will be briefly described below. Chemical VaporDeposition (CVD) is the formation of a stable compound on a heatedsubstrate, such as a wafer, by the thermal reaction or deposition ofvarious gaseous compounds. Epitaxial deposition is the deposition of asingle crystal layer on a substrate (often of the same composition asthe deposited layer), whereby the layer is an extension of the crystalstructure of the substrate. Another example of CVD is generallyclassified as metallization wherein the processed silicon substrateshave the metal connectors and the like deposited thereon. In an ionimplantation process, selected ions of a desired dopant are acceleratedusing an electrical field and then scanned across the surface of a waferto obtain a uniform predeposition. Batch processing systems involve thedeposition of more than one substrate or wafer at a time.

In the batch processing, the wafers are carried in boats and the boatsare usually loaded and unloaded as by use of tweezers, hand-held vacuumpick ups and the like. Loading robots may be used to transfer multiplewafers simultaneously. While batch processing systems have been usedextensively, the modern trend is toward the use of single wafertransport systems in order to process ever larger semiconductor wafershaving diameters of over 30 centimeters. These larger wafers can containmany more circuits and much more complex circuits than were heretoforepossible. While single wafer systems have less throughput than batchprocessing systems, attempts are being made to speed up the single waferprocesses, to develope higher yields, to avoid problems such as particlecontamination and to increase uniformity and quality.

Most known single wafer transport mechanisms can be adapted for use invarious types of semiconductor processing systems. Such transportmechanisms include the following. In a gravity feed transport system,the wafers are stacked in a supply receptacle, which receptacle issupported in an elevator at an angle to vertical; the wafer within thereceptacle is free to slide out and along an inclined ramp to a vacuummandrel. A second inclined ramp is provided to permit a processed waferto slide down the second ramp into a receiving receptacle. Thedisadvantages of this type of mechanism include the lack of positivefeed; the material placed onto the wafer can come off on contact withthe ramps; contaminating particles may be generated by the ramps; and,it may be limited to a single size wafer. Another type of semi-automaticmechanism for transporting wafers utilizes air bearings. The wafers aremaintained horizontal and are transported to and from the processingarea upon a cushion of air. This type of mechanism has proven to behighly unreliable and includes many moving parts subject to breakage andmaintenance down time. Foreign material may enter and damage the airbearings or reduce their effectiveness. Other transport mechanismsutilize air cushion guidance devices where the problem of cleanliness ofthe air and of the turbulence produced by the air cushion are quitesignificant. The settling of airborne particles onto the top surface ofthe wafers is difficult to avoid in air cushion systems. Further,lateral guard rails must be used, and contact between the edges of thewafer and the guard rails occurs frequently and may result inunacceptable contamination or damage to the wafers. Finally, only onesize of wafer can be handled without significant modification and downtime occurs when the wafer receptacles are being replaced manually.

Various mechanical transport systems have been used. One system uses arotating carousel in combination of supply and receiving slides. Anothersystem uses a belt drive transport to discharge the wafers from a supplycassette and at various other transfer points. As the cassettes aredischarged successively from the bottom and loaded in reverse order,impurities often drop from the bottom of one wafer onto the top of thewafer beneath it. Additional problems arise at the transfer pointsbecause the transport motion of the wafers is terminated by stopperswhich can result in previously deposited layers being spalled off orchipped off to further contaminate the wafer surfaces. Other waferhandling systems utilize a spatula or shovel type pick up to slide underthe wafers or move under the wafers and come up through the cassettetrack spaces to pick up the wafers and carry them to the next location.

An arm type system utilizes a vacuum chuck positionable under a waferfor attachment to the underside of the wafer by producing a vacuum atthe point of contact. The wafer is lifted out of the cassette andcarried to a processing station or the like; this system cannot place awafer on a flat continuous surface. Damage often results from themechanical contact between the vacuum chuck and the wafer.

In summary, the trend of the prior art is toward single wafer processingsystems. A key factor in automating such systems lies in improving thewafer transport mechanism. Furthermore, the critical problems presentedby particle contamination become ever more important as wafers becomelarger and larger and as circuits become more and more complex. None ofthe known systems are sufficiently clean to enable their use in acompletely automated processing system, nor do they avoid touching thetop and/or bottom surfaces of the wafer.

SUMMARY OF THE INVENTION

A pick up wand assembly of the present invention utilizes the BernoulliPrinciple for effecting a contactless pick up or lifting of the wafer.The wand assembly is mounted at the front of a robot arm, which armincludes passageways for receiving and distributing a gas to the pick upwand assembly. A plurality of gas outlets in a bottom plate of the pickup wand assembly produces an area of relatively low pressure between thetop surface of the wafer and the bottom surface of the pick up wandassembly (with respect to the pressure existing beneath the wafer) forlifting the wafer without physical contact between the wafer and thepick up wand assembly. The plurality of gas outlets are oriented orslanted substantially radially outward from a central portion of ageometric pattern to produce an outward gas flow across the top surfaceof the wafer to be picked up. The gas flow: (1) establishes a zone ofrelatively low pressure between the bottom plate and the top surface ofthe wafer (relative to the pressure normally existing beneath the lowersurface of the wafer) to enable a pick up from above the wafer withoutany physical contact between the wafer and the bottom plate; (2)provides a continuous outward sweeping action which sweeps the topsurface of the wafer free of particles which might otherwise accumulate;(3) provides a uniform gap between the bottom plate and the top surfaceof the wafer; (4) exerts a soft gentle horizontal force on the wafer formoving it toward stops; and (5) avoids abrasion and damage to the wafer.

A primary object of the present invention is to provide a wafertransport mechanism employing a wafer pickup wand utilizing theBernoulli Principle.

Another object of the present invention is to provide a wafer handlingsystem utilizing a pick up wand for lifting a wafer without physicalcontact therebetween.

Yet another object of the present invention is to provide a wafertransport mechanism which greatly reduces particulate generation.

Still another object of this invention is to protect the top surface ofa wafer from particulate contamination during pick up, transport, anddrop off.

A further object of this invention is to provide a pattern of gasoutlets on the bottom of a pick up wand for substantially, radiallyoutwardly, directing the gas flow to provide for the creation of a lowpressure area between the lower surface of the pick up wand and theupper surface of the wafer to enable the wafer to be picked up fromabove and without physical contact therewith while simultaneouslyproviding an outward flow of air which flow continually sweeps thesurface of the wafer to prevent contamination from particles.

A further object of the present invention is to provide a pick up wandwhich, by means of a particular pattern of outwardly oriented gasoutlets, creates an outward gas flow at all points on the waferperimeter to avoid drawing in particulate contaminants from thesurroundings onto the wafer while creating a force to lift the wafer.

These and other objects of the invention will become apparent to thoseskilled in the art as the description thereof proceeds.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the wafer transport mechanism of thepresent invention as utilized in a semiconductor processing system;

FIG. 2 is a partially sectional top plan view of the wafer transportmechanism shown in FIG. 1;

FIGS. 3A-3P show a series of illustrations depicting the movements ofthe robot arms shown in FIG. 1;

FIG. 4 is an assembly drawing of the drive system;

FIG. 5 is an assembly drawing of the fluidic drive portion of the drivesystem shown in FIG. 4;

FIG. 6 is a sectional top view of the gear drive portion of the drivesystem shown in FIG. 4;

FIG. 7 is a top view of the robot arms shown in FIG. 1;

FIG. 8 is a side view of one of the robot arms shown in FIG. 7;

FIG. 9 is a perspective view of the pick up wand assembly shown in FIG.1;

FIG. 10 is a sectional side view of the front end of the robot armsshown in FIG. 9;

FIG. 11 is an assembly drawing illustrating the front end of the robotarms the pick up wand assembly shown in FIG. 9;

FIG. 12 is a bottom view of the gas distribution plate shown in FIG. 9;

FIG. 13 is a sectional end view of the gas distribution plate shown inFIG. 12;

FIG. 14 is a sectional side view of the gas distribution plate shown inFIG. 12;

FIG. 15 is a top plan view of the plate shown in FIG. 9;

FIG. 16 is a sectional side view of one of the gas outlets shown in FIG.15;

FIG. 17 is a sectional side view of a gas outlet shown in FIG. 15;

FIG. 18 is a partial sectional side view showing an apparatus forfurther reducing particle contamination; and

FIG. 19 is a partial sectional side view showing apparatus for particleelimination.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The wafer transport mechanism described herein may be used in anepitaxial deposition system but it can be used in other types ofsemiconductor processing systems.

Referring to FIGS. 1 and 2, substrate transport mechanism 21 includes alaminar flow envelope or enclosure 23 having a substantially hollowinterior 25. Preferably, the enclosure is made of a non-contaminatingmaterial, such as anodized aluminum. The epitaxial deposition system inwhich substrate transport mechanism 21 is usable includes a reactoroven, reaction chamber, or reactor 27 having an access slot 83 toprovide communications between hollow interior 25 with hollow interior63 of the reactor. A gate valve (not shown) is provided for selectablyopening or sealably closing access slot 83.

The epitaxial deposition system includes at least two purge boxes orstations 29, 31 for supplying wafers 81 to be processed and for storingthe wafers after they are processed, respectively. Each of stations 29,31 includes a hollow interior and one of access slots 35, 37,respectively, for communication with enclosure 23. Each of stations 29,31 also includes a cassette 33 which sits on an indexing elevator. Eachcassette includes a plurality of vertically stacked tracks forhorizontally supporting the substrates or wafers on their outermostperipheral edges. Each wafer may be a six inch circular silicon waferwhich is to have additional silicon deposited thereon. Each station 29,31 also has an access door (not shown) on the side opposite therespective slot for human operator access to load and unload thecassettes.

The specific structures of stations 29, 31, cassettes, wafers,elevators, elevator indexing mechanisms, purging system and the like,are not critical to an understanding of the present invention and willnot be described in any greater detail.

An arm mounting plate assembly 39 is disposed in a central recess infloor 45 of enclosure 23 and is used to operatively mount the rear endof a pair of robot arms 41 thereto. The combination of plate assembly 39and individual shaft drives to the rear end of robot arms 41 enables therobot arms to be extended and retracted toward and away from the plateassembly and to be angularly repositioned from location to location,such as from station 29 to reactor 27, or the like. A pick up wandassembly 43 is operatively mounted to the front end of robot arms 41 foractually picking up or lifting wafers 81 for transport purposes.

Enclosure 23 includes a floor 45, a top surface 47, a first longitudinalside 49, a second longitudinal side 51, a first end side 53, a secondend side 55, and a rear end side 57. Plate assembly 39, together witharticulated robot arms 41 and the wand assembly 43, are all housedwithin the hollow interior of enclosure 23. Plate assembly 39 is mountedin a recess in floor 45 and driven by a drive assembly which isvacuum-sealed on the opposite side of the floor, as hereinafterdescribed. Hollow interior 25 is adapted to provide a controlled cleanatmosphere and the atmosphere is preferably one of hydrogen, nitrogen orargon.

FIG. 2 particularly illustrates robot arms 41 in various positions ofextension and retraction from plate assembly 39. In a first position,the robot arms are designated by the reference numeral 65 and the wandassembly by reference numeral 67. In this position, wand assembly 67 isat its closest position to plate assembly 39 and this is referred to asthe home position since it is only in this position that the plateassembly rotates to rotatably position the wand assembly from locationto location. Reference numeral 69 illustrates the robot arms in a secondposition that the wand assembly 71 would occupy. A third position isindicated by reference numeral 73 which positions wand assembly 75 justinside of access slot 83 of reactor 27. Lastly, robot arm position 77shows the pair of robot arms fully extended to position wand assembly 79within hollow interior 63 of reactor 27 and over the susceptor fordelivering wafer 81 thereto.

FIGS. 3A-3P illustrate the various positions of robot arms 41 withrespect to wand assembly 43 and plate assembly 39. In each of thesefigures, a portion of enclosure 23 will be shown with at least one ofstations 29, 31 or reactor 27. Directional arrows are provided to showeither the direction of extension, the direction of retraction, or thedirection of rotation during any one step, as represented by theindividual figures.

In FIG. 3A, robot arms 41 are shown in their home position with wandassembly 43 facing station 29 and containing at least one wafer 81 to bepicked up. In FIG. 3B, robot arms 41 have begun to extend away fromplate assembly 39 and toward wafer 81. Directional arrow 85 shows thelinear direction of movement during the wafer pick up operation. FIG. 3Cshows robot arms 41 in their fully extended position with wand assembly43 positioned through access slot 35 and into purge box 29 for pickingup wafer 81 from a cassette on an elevator housed therein. FIG. 3D showsrobot arms 41 in an intermediate position of retraction (as indicated bythe directional arrow 87) after pick up of wafer 81, toward the homeposition shown in FIG. 3E. In FIG. 3E, robot arms 41 are again in thehome position and ready for the rotational movement indicated by therotational direction arrow 89 shown in FIG. 3F. In this position, therobot arms are in the home position and plate assembly 39 is rotatedcounterclockwise from station 29 toward the reactor 27.

In FIG. 3G, robot arms 41 are still in the home position but wandassembly 43 now faces access slot 83 of reactor 27. In FIG. 3H, therobot arms are again shown in an intermediate position while movingwafer 81 toward reactor 27, as indicated by directional arrow 91 showingthe linear direction of movement from this position. FIG. 3I shows robotarms 41 in a fully-extended position such that wand assembly 43 canposition or deposit wafer 81 onto the susceptor within reactor 27. FIG.3J shows robot arms 41 at an intermediate position of retraction, asindicated by the directional arrow 93 and FIG. 3K shows the robot armsreturned to their home position.

In FIG. 3L, plate assembly 39 again rotates counterclockwise, asindicated by directional arrow 92, to rotationally reposition wandassembly 43 and processed wafer 81 from reactor 27 and toward the accessslot 37 of station 31. In FIG. 3M, robot arms 41 are in the homeposition with wand assembly 43 facing access slot 37 of station 31. InFIG. 3N, the robot arms are shown in an intermediate position ofextension as they move toward access slot 37 of station 31, as indicatedby directional arrow 94. In FIG. 30, the robot arms are fully extendedinto station 31 to deposit wafer 81 on the tracks of a cassette locatedtherein. In FIG. 3P, the robot arms are shown in an intermediateretracted position as they once again return to the home position shownin FIG. 3M, as reflected by directional arrow 96.

FIG. 4 illustrates drive assembly 101 for extending and retracting robotarms 41 and rotating plate assembly 39. Rotatable plate 131 is agenerally flat, circular plate which is operatively disposed within acylindrical recess (not shown) located in floor 45 of enclosure 23. Apair of screw members (not shown) pass through apertures 140, 142 andsecure plate 131 to the drive mechanisms therebelow while a pair ofshafts 133 and 135 extend vertically above the plane of plate 131.

Shaft 133 is adapted to engage an aperture 144 in rear end connector 145of robot arm segment 139 while the upper end of shaft 135 engagesaperture 146 of end connector 147 at the rear end of second robot armsegment 141. Each of the lower robot arm segments is shown as being agenerally elongated member having a conduit 143 for gas flowtherethrough.

Drive assembly 101 includes a shaft drive motor 103 which is aconventional DC, digital, micro-stepping motor (such as Model No.M062-FC03E manufactured by Superior Electric Co. of Bristol, Conn.).Robot arm drive motor 105 is a digital DC micro-stepping motor (such asModel No. M092-FC08E manufactured by the Superior Electric Co. ofBristol, Conn.). Drive motor 103, which is used for the extension andretraction of robot arms 41, drives a flex shaft coupler, 124 (397 FIG.5) which drives the ferrofluidic feedthru 409 which has a gear 167 andcollar 171 attached to the gear box end (FIG. 6) of the feedthru shaft.Gear 167 then drives gear 165 (shaft assembly 135) which through shaft135 drives gear 163 which then drives countershaft 133 by way of gear161 in the opposite direction of shaft 135. Drive motor 105, which isused for the rotation of robot arms 41 and having a shaft 109 which hasa drive pulley 111 mounted to it, drives belt 113 which drives pulley115. Pulley 115 is attached to drive tube 122 which has motor 103,flange 123 mounted on the bottom and feedthru 409 and the gear boxassembly (FIG. 6) mounted on the other (top) end. This drive tube isthen mounted in the hollow shaft of feedthru 125. Pulley 115 has acollar 117 extending from the top surface; a channel 119 passes throughthe collar and the pulley. Drive shaft 121 of drive motor 103(extension, retraction motor) extends vertically upwardly therefromthrough internally-threaded collar 123 disposed on the upper surface ofthe housing of drive motor 103, a nut 128, channel 119, collar 117,through the interior of a vertically downwardly extending tubular stem120 having an externally-threaded end portion 122 and into ferrofluidicdrive housing 125 connecting to 409 (FIG. 5).

Ferrofluidic drive housing 125 will be more extensively described withjoint reference to FIGS. 5 and 6. Gear housing 127 is coupled through avacuum seal to interior 25 of enclosure 23. Robot arms 41, via the shaftextensions 133 and 135, are driven to extend and retract via theoperation of the gears cooperating with ferrofluidic drive shaft 409,121. The rotation of plate 131 of plate assembly 39 will no bedescribed. The externally-threaded end 122 of stem 120 is insertedthrough channel 119, through nut 128, and threaded into collar 123. Nut128 can be used as an adjustment or lock nut. Once end 122 is screwedinto collar 123, pulley 115 is securely clamped to stem 120 and may bepinned by a pin extending through aperture 118 of collar 117 and acorresponding aperture (not shown) in stem 120. As motor 105 drivespulley 115, stem 120, which is fixedly secured to the bottom center ofhousing 125, rotates housing 127 supported by bearings in feedthru 125.

Ferrofluidic base plate 390 is shown in FIG. 5 a being attached to ametal bellows assembly 393 over which is mounted plate 132. Plate 132includes a ring 395, an aperture 400 and a pair of elongated members396. A motor-mounting plate 399 is disposed on elongated members 396extending from ring 395. A hollow tubular stem or ferrofluidic drivetube assembly 401 includes stem 120 and an annular flange 405.Intermediate connector 397 passes inside of the threaded end of stem 120and the base of tube assembly 40 is operatively disposed within thehollow central drive channel 388 of base plate 390. A ferrofluidic driveshaft 172 extends from the top surface of annular flange 405, through aferrofluidic collar 409 to a pinion gear 167 and its shaft 171 disposedin housing 127. Shaft 172, tube assembly 401 and collar 409 comprise aferrofluidic feedthrough mechanism 407 which brings about extension andretraction of robot arms 41.

The ferrofluidic drive apparatus described above is a commerciallyavailable conventional unit adapted herein to enable extension andretraction of the robot arms and rotational movement of plate assembly39. Connector 397 passes through aperture 400 of mounting plate 132 andchannel 384 of bellows assembly 393 to engage channel 388 in base platemember 390. Channel 388 is surrounded by a collar 386 that is housedwithin a larger channel 384. Plate 399 is disposed on elongated members396.

Tube assembly 401 includes a shaft 403 and annular flange 405. Athreaded end 404 connects connector 397 inside the threaded end of shaft403 and the base of tube assembly 401 is operatively disposed within thechannel of plate member 390. Tube assembly 401 passes shaft 171 throughthe top surface of annular flange 405 which is surrounded by a threadedend 411 and an outer collar 409.

FIG. 6 illustrates the gear assembly within housing 127. The gearassembly includes an outer cylindrical wall 151 mounted onto mountingplate 132. The mounting plate is attached by means of bolts 157 to thetop portion of housing 125. Interior 153 of wall 151 receives driveshaft 171 from housing 125 and drives pinion gear 167. Pinion gear 167engages with the teeth of gear 165 which gear is coupled via shaft 135to drive gear 163. The teeth of drive gear 163 mesh with the teeth ofgear 161 mounted on shaft 133. Shafts 133 and 135 each have an upperextending end which extends through the upper surface of plate 131 intoenclosure 23 to engage the rear end of a corresponding one of armsegments 139 and 141, as shown in FIG. 4. In this manner, extension andretraction of the arms are accomplished by the respective rotation ofshafts 133 and 135 and via the rotation of gears 161 and 163,respectively.

FIG. 7 shows robot arm 41 in greater detail. Rear end 175 of each of thepair of robot arms includes a member 181 having an aperture 177 forengaging the extending portions of shafts 133 and 135. Rear end 175includes a hex head self-locking clamp mechanism with a head 183 havingan elongated, externally-threaded stem 185 for engaging a hollow,internally-threaded retainer drum clamp 187 to tighten or loosen thegrip of member 181 about respective shaft 133 or 135. Furthermore, eachof rear ends 175 of arm segments 139 and 141 includes a gas inletcomprising an elongated cylindrical stem 189 and an interior channel 191communicating with hollow interior 186 of arm segments 139, 141. Inletchannel 191 is connected to a source of gas, such as hydrogen ornitrogen.

Each intermediate portion of arm segments 139 and 141 includes agenerally cylindrical wall 188 and each has a hollow interior 186 or atleast a hollow interior gas-conducting passage within the hollowinterior. An arm mid-connector 193 includes shaft 197 for engaging anopposing mid-connector 195 of upper arm assemblies 199 and 201,respectively. Each of the upper arm assemblies has a substantiallyhollow interior 203 and a cylindrical wall 205. At each end of upper armassemblies 199 and 201 is disposed an end plate 207, 209, respectively.Each of end plates 207, 209 is connected to a Bernoulli mounting plate211 through gear segment 213 and gear segment 215, respectively. Theteeth of the gear segments mesh at a point designated by numeral 217. Aretainer bushing 219 includes a gas passageway 221 and a pair ofapertures 223.

FIG. 8 shows a side view of one of robot arms 41. Rear end 175 includesdrum clamp 187 having a threaded internal aperture 227 extendingtherethrough. The rear end also includes a gas flow inlet, stem 189having an inlet channel 191 for communicating with an external source ofgas. The front end of arm segment 139 is connected via mid-connector 193and shaft 197 to mid-connector 195; bearings 223 are retained aboutshaft 197 and by a nut 231.

An intermediate portion of arm assembly 201 includes a filter 229operatively disposed within interior 203 for filtering particles fromthe flow of gas passing therethrough. The gas is channeled through endplate 209 and then upwardly through a bearing 219 via passageway 221 tomounting plate 211. FIG. 9 illustrates the front end of robot arms 41,mounting plate 211 and wand assembly 43. Arm assemblies 199 and 201 arecoupled to mounting plate 211 via end plates 207 and 209, respectively.The wand assembly is connected to the under surface of mounting plate211 by a wand retainer plate 299. The wand assembly includes a gasdistribution plate 293 and a gas outlet plate 295 which may be referredto collectively as the head unit. Each of the plates 293 and 295 issubstantially flat or planar and is adapted to have one surface mountedflush against a surface of the other. Gas distribution plate 293 has aflat upper surface 296 and gas outlet plate 295 has a flat or planar topor upper surface 298. Preferably, plates 293 and 295 are made of fusedquartz and acid-etched with hydrofluoric acid to greatly reduce atendency to produce or attract particles which might contaminate ordamage the wafers.

FIG. 10 shows a sectional side view of arm assembly 201 of one of thepair of robot arms 41, including end plate 209 and mounting plate 211.Interior 203 of the robot arm includes a gas-conducting passageway whichcommunicates with a smaller diametered cylindrical gas inlet passageway245 in the front of end plate 209. End plate 209 includes a metal,preferably stainless steel or some similar structural material, body 241secured within the interior walls of arm assembly 201. O-ring gaskets267 are housed in annular slots 265 to prevent the escape of gas. Armassembly 201 is connected to end plate 209 and body 241 of the end plate209 via fastener 269.

A relatively narrow, cylindrical gas-conducting conduit 247 communicateswith passageway 245 and a vertical gas passageway 249. Passageway 249 issurrounded by a lower retainer 277 and an upper retainer 279. A collar291 and bearing 275 surrounds passageway 249 and are connected viathreaded fasteners 281 to mounting plate 211. Another fastener 271 isused to secure gear segment 215 to body 241 of end plate 209.

The gas flows through a narrow, gas-conducting, slanted passageway 247to horizontal gas collection chamber 278 and then flows verticallyupwardly through passageway 249, through an outlet 283, and into ahorizontal passageway 251 of mounting plate 211. The mounting plateincludes a body 273 having a generally cylindrical recess 255 formed inthe front end. Floor 266 of recess 255 includes a gas outlet aperture263. The gas outlet aperture 263 communicates with an inlet 317 in uppersurface 296 of gas distribution plate 293. Gas inlet 317 communicatesthrough gas distribution plate 293 via channel 329 to a bottom gasoutlet 321. Floor 256 of recess 255 has an annular filter 261 disposedtherein for filtering particles from any gas passing therethrough viathe inlet 257 and aperture 263. An annular member 292 is positioned withan annular flange 294 disposed about the outer peripheral edge portionof the filter 261. Upper shoulders of the annular member 292 contain anannular groove 288 for housing an O-ring seal 287. Annular member 293 iscompressively held within recess 255 via a cover 289 secured within theopening 285 for replacing filter 261. The gas flows horizontally throughthe rear portion of mounting plate 211 via passage 251 and then passesdownwardly through short, narrow, slanted passageway 253 into recess 255about annular flange 294. The gas then passes through inlet 257 of theannular flange and enters into hollow central cylindrical cavity 259from whence it passes vertically downwardly through aperture 263 to gasdistribution plate 293.

FIG. 11 shows the front end portion of robot arm 41, mounting plate 211and wand assembly 43. The connection between arm segment 139 and armassembly 201 includes mid-connector 193, mid-connector 195 and shaft 197therebetween. Arm segment 139 is attached to mid-connector 193. Themid-connector includes a cylindrical body 430 integral with arectangular block 427. A sleeve 432 surrounds body 430. The cylindricalbody terminates at gas inlet 421. Gas travels from the gas inlet througha cylindrical central passageway 423 to a relatively small circular gasoutlet 425. Outlet 425 communicates through a narrow passageway 422 witha second gas outlet 429.

Block 427 of the mid-connector 193 includes a cylindrical channel 433for housing a gas inlet sleeve 431 therewithin the interior thereof.Sleeve 431 includes a channel 434 communicating with outlet 429 of gaspassageway 422 through an aperture (not shown) in the cylindrical wallof sleeve 431. Sleeve 431 is housed within a cylindrical channel 433 ofblock 427 of mid-connector 19 via a bottom seal 435, a collar 437, awasher 439, and a nut 441, each of which has a central aperture forreceiving at least threaded end 451 of shaft 197. Threaded end 451 ofshaft 197 is threadedly engaged with nut 441. To secure the upper end ofsleeve 431 within channel 433, an upper seal 435, an upper collar 443,and an upper washer 445 are provided.

Shaft 197 includes a shaft 452 having a threaded end 451 supporting anouter sleeve clamp 453. An inner sleeve clamp 455 is secured to thebottom of body 460 of mid-connector 195. Midconnector 195 has a verticalcylindrical channel 459 extending therethrough and a top opening 457.This portion receives at least a portion of the top of shaft 197 suchthat arm segment 139 and arm assembly 201 are articulated or renderedpivotable about shaft 452. Mid-connector 195 also includes an integralcylinder 464 surrounded by a sleeve 463 and defining channel 466.Channel 466 connects to the mid-portion of arm assembly 201 and conveysa flow of gas from channel 466 to interior 203 of arm assembly 201.Interior 203 of the arm assembly 201 is defined by inner sleeve 469 andouter sleeve 467.

The cylindrical plug 473 of end plate 209 is disposed within sleeve 467and attached through the drum clamp via apertures 476 and 478. End plate209 also includes a partial cylindrical end 474 which is sized to besecured to the front of plug 473. Cylindrical end 474 supports agenerally planar body 472 having a flat upper surface 475. The end platecontains a plurality of apertures 477 for receiving fasteners 495.

Body 472 includes a generally hollow cylindrical recess 479 therein. Therecess is adapted to receive lower retainer bushing 481 therein. Bushing481 includes a pair of outer apertures 483 adapted to receive screwfasteners therethrough and a central channel 485 which forms a verticalgas passageway for the assembly. A bearing 487 having a hollow interior488 is housed over the end portion or annular flange of lower retainerbushing 481. The upper portion of the interior 488 of bearing 487 isadapted to receive an upper retainer bushing 491. Bushing 491 alsoincludes a central gas channel 485 and a pair of fastener-receivingapertures 483 on either side of the channel. The top of retainer bushing491 is adapted to be received within central aperture 497 of gearsegment 215. The gear segment includes a body 496 having a plurality ofgear teeth 498. A straight edge 600 and intersecting edge 602 form theother sides of gear segment 496. The gear segment is provided with aplurality of apertures 499 for receiving fasteners 495.

Mounting plate 211 includes a generally rectangular blocklike member 494having a first relatively thin, generally rectangular, rear part 493 anda second somewhat thicker, generally rectangular, front part 500.Threaded fasteners 523 extend through a plurality of apertures 507 inrear part 494 and apertures 497 of body 496 to engage apertures 483 ofupper and lower bushings 491 and 483. A gas passage 511 (of which theexterior is shown) passes longitudinally through the rectangular rearpart of mounting plate 211 for receiving the gas by communicating withcentral aperture 485 of upper bushing 491.

Passage 511 extends into front part 500 and then through a gas inlet 503into a generally cylindrical cavity 501. Cavity 501, including acylindrical wall 502, has a floor 504 which is provided with a pluralityof interconnecting gas outlets 505. Threaded apertures 509 in floor 504receive conventional threaded fasteners (not shown) passing throughapertures 527 of cover plate 525 for closing the top of cavity 501. Gasinlet 503 is disposed a predetermined distance vertically above outlets505, and a disk-like filter element 515 is placed on the bottom of thecavity to filter any gas passing through the cavity from inlet 503 tooutlet 505. Above filter 515, a filter plunger 519 is disposed withincavity 501, and on top of the plunger is seated an O-ring seal 517 whichfits about an annular collar portion of the plunger. Cover plate 525 isplaced over top surface 512 of front part 500 to retain plunger 519 andfilter 515 in place within cavity 501 while preventing escape of gasfrom the cavity. Outlets 505 of cavity 501 pass through bottom 510 andcommunicate with aperture 531 in a central portion of gasket 529, whichgasket has a plurality of apertures 533 on the edge portions forreceiving conventional fastener means. Bottom surface 532 of gasket 529is adapted to be placed over the rear end of upper surface 296 of gasdistribution plate 293 to align apertures 533 with apertures 313 of thegas distribution plate and gas passage aperture 531 with ga inletaperture 319 of the upper gas distribution plate.

Gas distribution plate 293 includes a generally planar upper surface 296and a relatively planar lower surface 333. The top surface includesaperture 319 proximate rear end 305. A plurality of apertures 313 areincluded on both rear edges for securing gas distribution plate 293 tobottom 510 of front part 500 of mounting plate 211 through apertures 533of gasket 529.

The portions shown in dotted lines represent the array or pattern of gasdistribution channels or grooves formed on lower surface 333 of gasdistribution plate 293. The pattern of gas distribution grooves includesa first elongated longitudinal side groove 323, a second elongatedlongitudinal side groove 327 and a lateral groove 331 connecting thediverging ends of the side grooves. Side grooves 323, 337 and lateralgroove 331 form an isosceles triangle having an apex terminating in acommon reservoir or channel 329 communicating with aperture 319 in gasdistribution plate 293. A central, elongated, longitudinal channel orgroove 325 may be provided to bisect the isosceles triangle alonglateral groove 331 at its mid-portion. The gas supplied to aperture 319is distributed to each of grooves 323, 325 and 327 and therefrom togroove 331.

Gas outlet plate 295 includes a relatively planar upper surface 298 anda relatively planar lower surface 355. Apertures 341 proximate rear end343 are adapted to be aligned with apertures 537 of retainer plate 539,forward apertures 313 of gas distribution plate 293, forward apertures533 of gasket 529, and a forward pair of apertures 509 in front part 500of mounting plate 211. Fastener means passed through these aperturessecure gas distribution plate 293 and gas outlet plate 295 flush againstone another in a sandwich-type configuration.

Upper surface 298 of gas outlet plate 295 includes a geometric pattern601 for gas distribution. Each of the outlets is shown on upper surface298 of gas outlet plate 295 as including a circular opening contained onor within a boundary of pattern 601. The pattern can be thought of asbeing similar to a four-sided geometric figure such as a truncatedisosceles triangle. The base of the triangle can be thought of asexisting between the imaginary intersections defined by points 611 and613 and interconnected by a base 603 of triangle 610. The sides of thetriangle can be thought of as terminating at rear end 343 of gasdistribution plate 295. An imaginary line between gas outlets located onthe opposed sides of the triangle define truncated top 605. The sides oftriangle 610 coincide with the geometric pattern of grooves on lowersurface 333 of gas distribution plate 293.

Side 607 of truncated triangular pattern 601 is connected betweenimaginary intersection point 613 and outlet 361 while opposite side 609of truncated triangular pattern 601 is connected between imaginaryintersection point 611 and outlet 366. This forms a truncated rightisosceles triangle having base 603, truncated top 605, and pair of sides607, 609.

A pattern of seven gas flow outlets are located or disposed on theborder defining the truncated triangle. A first outlet 361 is formed atthe intersection of side 607 with top 605 and outlet 366 is formed atthe opposite end of top 605. A third gas outlet 362 is disposed on side607 closer to imaginary intersection 613 than to outlet 361. A fourthgas outlet 365 is disposed on side 609 closer to imaginary intersection611 than to outlet 366. A fifth outlet 363 is formed on base 603 betweenthe imaginary intersection 613 and the longitudinal axis of wandassembly 43. Equally spaced on the opposite sides of the longitudinalaxis is a sixth gas outlet 364 located approximately in the middlebetween the longitudinal axis and imaginary intersection 611. Lastly, aseventh gas flow outlet 367 is disposed on the longitudinal axis at themidpoint of top 605.

Each of outlets 361, 362, 363, 364, 365, 366 and 367 communicates with acorresponding gas flow outlet on lower surface 355 of gas outlet plate295, and each is interconnected therewith through a slanted or taperedintermediate channel portion. The tapered channel connecting thelaterally displaced upper and lower outlets enables the seven gas flowoutlets located on the periphery of pattern 601 to direct the gas flowsubstantially radially outwardly from a central portion of the patternso that the gas flow is directed substantially radially outwardly acrossthe top surface of wafer 81 to be picked up and to provide the necessaryconditions to effect application of the Bernoulli Principle. The gasflow across the top surface of the wafer creates or establishes an area,volume, or zone of relatively low pressure between lower surface 355 ofgas outlet plate 295 and the top surface of wafer 81 with respect to thepressure existing at the bottom surface of the wafer. This pressuredifferential serves to lift the wafer without any physical contactwhatsoever between wand assembly 43 and the top or bottom surfaces ofwafer 81.

Furthermore, this pattern provides a continuous outwardly sweeping flowof gas across the top surface of the wafer which greatly reduces thenumber of particles or contaminants which can collect thereon. Some veryslight, soft contact can occur between two spaced apart areas on theouter peripheral rim of wafer 81 and a pair of depending locators 543.Locators 543 are disposed on the rear end of lower surface 355 of gasoutlet plate 295 adjacent sides 345 and 347 thereof. An importantfunction of the array of gas outlets is to bias the gas flow to draw thewafer slowly rearwardly under gas outlet plate 295 until the wafer'souter peripheral edge make soft contact with front sides 542 of locators543. This soft gentle contact is not between the top surface of thewafer and the bottom surface of gas outlet plate 295, but only with twosmall areas on the outer peripheral circumference of the wafer andlocators 543. The above-mentioned rearward horizontal bias results fromthe orientation of the gas outlets in the pattern in which only two ofthe seven outlets are radially outwardly directed in a forward directionwhereas five of the seven outlets are radially outwardly directed in arearward direction. This creates a horizontal component of force tendingto urge the picked-up wafer rearwardly until it makes soft contact withlocators 543.

When lower surface 333 of gas distribution plate 293 is placed over andflush against upper surface 298 of gas outlet plate 295, all of outlets361, 362, 363, 364, 365, 366 and 367 are operatively disposed directlybeneath the pattern of grooves 323, 325, 327 and 331 formed on lowersurface 333 of gas distribution plate 393 for supplying a flow of gasthereto.

Additionally, a central outlet 368, which is supplied with gas fromcentral longitudinal groove 325 in lower surface 333 of gas distributionplate 293, is located approximately in the center of the geometricpattern along the longitudinal axis of gas outlet plate 295 and is,contrary to the other gas outlets, disposed at a 90° angle straightthrough the gas outlet plate. The flow of gas from this outlet serves toaid in substantially reducing or eliminating turbulence, rapid verticaloscillations or wafer dribbling, and in substantially totallyeliminating the pick-up of contaminant particles which would otherwiseresult from a "vacuuming effect".

Lower retainer plate 539 is disposed beneath lower surface 355 of gasdistribution plate 293 and apertures 537 are aligned with apertures 341of gas outlet plate 295, apertures 313 of the gas distribution plate,apertures 533 of upper retainer plate 529 and the apertures in lowersurface of front part 500 of mounting plate 211. Conventional fastenerssecure these elements securely together in a sandwich-like manner. Tape535 with corresponding aperture 538 insures a firm contact between uppersurface 536 to lower surface 355. Fasteners, not shown, pass upwardlythrough the assembly and screw into the bottom of mounting plate 211.The removal of a few fasteners enables one wand assembly for use with awafer of a first diameter to be easily interchanged with another wandassembly for use with a wafer of another diameter.

FIG. 12 shows lower surface 333 of gas distribution plate 293. Aperture319 communicates with inlet 317, which inlet communicates via outlet 321with the commonly connected ends of the grooves. The commonly connectedor overlapping ends of the groove form channel 329 (discussed above) andthe gas from outlet 321 passes into the channel from whence it is fedinto and along each of the plurality of grooves.

FIG. 13 shows a sectional end view of lower surface 333 of gasdistribution plate 293. The gas distribution plate includes a single,integral, substantially flat member 301 of fused quartz and has arelatively planar top surface 302 and a relatively planar lower surface333. Sides 303 and 304 represent the sides between which the section istaken, to illustrate the cross section of grooves 323, 325 and 327.

FIG. 14 shows a longitudinal cross section of the gas distribution plate293. Rear end 305 is disposed across the longitudinal axis whichterminates at front end 311. The front end includes a relatively planarfront edge 337 of flat lower surface 333, a tapered top surface 335, anda pointed tip 339. Aperture 319 can be seen as being operativelydisposed in upper surface 296 of ga distribution plate 293 proximaterear end 305. Outlet 321 communicates with aperture 319 through channel329. The present section is taken through groove 325. At the end of thecentral longitudinal groove 325, the intersection with lateral groove331 is shown.

FIG. 15 shows a top view of gas outlet plate 295. The gas outlet plateincludes an upper surface 298, a relatively curved rear end 343, a pairof relatively straight sides 345 and 347, a pair of relatively straightfront ends 349 and 351, and a curved central front edge 353. Uppersurface 298 of gas outlet plate 295 is relatively planar and includesonly a plurality of outlets 361, 362, 363, 364, 365, 366 and 367. Theseseven outlets define pattern 601 while the common relief outlet 368 isdisposed in a central portion of the pattern for use as previouslydescribed. Upper surface 298 better illustrates the slope, taper orslant of the gas outlets and it will be noted that the flow is generallyradially outward from the approximate center of pattern 601 so as toprovide a continuous outwardly sweeping air flow for keeping particlesoff the top surface of the wafer while simultaneously providing the areaof decreased pressure for enabling the Bernoulli Principle to be used tolift or pick up the wafer without physical contact. Since five of theseven outlets are directed horizontally rearward, the wafer is slowlyurged horizontally rearwardly until it abuts locators 543.

FIGS. 16 and 17 illustrate the slanted channels described with respectto FIG. 15. The apertures are shown as having a circular inlet 371 onupper surface 298 of gas outlet plate 295, a circular outlet 375 onlower surface 355 and a sloped interconnecting channel 373. Similarly,the oppositely sloped gas outlets shown in FIG. 17 can be considered ashaving a circular inlet 377 in upper surface 298, a circular outlet 381in lower surface 355 and a sloped, slanted or tapered interconnectingchannel 379. The particular slope and orientation of the channel willdetermine the direction of gas flow from lower surface 355 of gas outletplate 295 and hence can provide the desired substantially radiallyoutward flow for maximizing the efficiency of the pick-up operationwhile simultaneously minimizing particulate contamination.

FIGS. 18 and 19 illustrate yet another embodiment of the wafer handlingsystem shown in FIG. 1 and add additional means for reducing particularcontaminants in the system. Enclosure 23 includes a top surface 47 and afloor 45 and a hollow interior 25.

As previously described, a portion of the drive assembly, such as gearhousing 569, is coupled through a vacuum seal to plate assembly 39 whichserves to drive a pair of articulated robot arms 41 having a pick-upwand assembly 43 mounted at the front end thereof for picking up andcarrying a semiconductor wafer 81. The rear ends of the articulatedrobot arms 41 are coupled to shaft 133 extending through floor 45 andplate assembly 39. A supply station, supply port or purge box (29)includes an elevator 551 for carrying a cassette holding a plurality ofwafers (not shown) in a horizontal position. Elevator 551 movesvertically in a step-wise linear manner to accurately position a waferat access slot 35 through which the robot arms pass to pick up a wafercontained in the cassettes for delivery to reactor 27.

In the embodiment shown in FIG. 18, a source 557 of ultraviolet (UV)infrared rays 560 is provided. The source may be any conventional tubeor other source of ultraviolet rays chosen to radiate in the desiredspectral range such that the UV rays pass readily through top surface47; the top surface is preferably made of fused quartz which istransparent to UV radiation at the radiating wavelength. Source 557 isprovided exterior of the top surface and UV rays 560 pass through thequartz and bombard the central area in interior 25 to continuallyirradiate robot arms 41, wafer pick-up wand assembly 43 and the topsurface of the wafer 81 carried thereby whenever the robot arms are inthe home position. Since the plates of the pick-up wand assembly arealso made of quartz, the UV rays pass readily therethrough to bombardthe top surface of the transported wafer and the area thereabove.Bombardment with ultraviolet rays 560 neutralizes the charge ofcontaminant particles within interior 25 of enclosure 23. By removingthe charge, the particles are less likely to interact with, stick to, beattracted to, or accumulate on the top surface of wafer 81. Thus,bombardment with ultraviolet rays reduces particle contamination andfurther improves cleanliness of the wafer handling system.

The UV source 557 is shown as having one terminal connected to a node558 which in turn is connected via lead 555 to one output of a powersource 553. The power source is also connected through a lead 556 to asecond node 559. Node 559 connects to the opposite end terminal of tube557 to supply power to the tube for generating the ultraviolet rays 560.

Alternatively, a tube 561 can be placed within interior 25 of enclosure23 adjacent top surface 47. The ultraviolet rays 563 perform thebombardment necessary for neutralizing charged particles which mightotherwise contaminate wafer 81. Tube 561 is supplied power via lead 565coupled between one end terminal of the tube 561 and node 558, whilenode 559 is coupled via lead 556 to the opposite end terminal of thetube 561.

FIG. 19 provides another embodiment of the concept shown in FIG. 18.Enclosure 23 includes upper surface 47 which may be a quartz panel, anda floor 45. Gear housing 569 is connected through a vacuum seal frombeneath the surface of floor 45 to interior rotatable plate assembly 39.The shaft 133 couples the gear housing with the rear end of a pair ofarticulated robot arms 41 to extend and retract them. Pick-up wandassembly 43 is shown as depositing wafer 81 onto a rotatable susceptor573 mounted on a pedestal 575 having a rotatable shaft 577. Theassembly, including susceptor 573, pedestal 575 and shaft 577, may beupwardly and downwardly positionable and rotatable, as desired. Robotarms 41 are in the fully extended position and to pass through gate 579communicating with interior 571 of reactor 27. Top 581 and bottom 583 ofreactor 27 are made from quartz to be transparent to ultravioletradiation of a particular wavelength or range of wavelengths.

A source of UV radiation, tube 592, is operatively mounted or disposedon the exterior of top 581 and arranged to irradiate the interiorproximate the entrance or between the gate and the susceptor of thereactor 27 to neutralize charged particle contaminants adjacent accessgate 579 and within the reactor. Tube 592 receives power from a powersource 587 and connected through a first lead 588 and a node 590 to oneterminal of tube 592. The power source is also connected through a lead589 to a node 591 and then to the other terminal of the tube.

In an alternate embodiment, the UV source or tube 596 is operativelymounted or disposed within the interior 571 of reactor 27 adjacent top581. Tube 596 produces UV radiation (rays 597) for bombarding the pathof wafer 81 from access gate 579 to susceptor 573 to neutralize chargedparticles and prevent them from accumulating on the wafer surface. Tube596 has one terminal connected via lead 594 to input node 590, and itsopposite terminal connected via lead 595 to input node 591 to obtainpower from power source 587.

In the preferred embodiment of the present invention, the pair ofarticulated robot arms are much stronger and more accuratelypositionable than was heretofore possible by constructing them ofstainless steel and providing them with a circular cross section. Thelength of the robot arms at their fully extended position issignificantly longer than the 18 inches normally possible and lengths ofat least 25 inches are routine.

Both gas distribution plate 293 and gas outlet plate 295 of pick-up wandassembly 43 are manufactured from fused quartz and acid-etched andpolished with an acid such a hydrofluoric acid. The etching andpolishing not only smooths and polishes the grooves and apertures formedin the plates to prevent particles from being deposited thereon, butalso polishes all the surfaces to prevent particles from being attractedto or accumulating on the surfaces and therefore reduce the chance ofcontaminating or damaging the wafer. The use of quartz for the waferpick up wand assembly enables it to be used to pick up relatively hotsubstrates. Normal processing in the reaction chamber raises the wafertemperature to approximately 1150° C. The temperature cools down tobelow 1000° C. in about one minute. A very short time later, when thewafer temperature is lowered to 800° C.-900° C., the pick up wandassembly can lift the hot wafer without damage thereto.

The walls of enclosure 23 are preferably made of a noncontaminatingmaterial such as anodized aluminum or the like and a window, preferablymade of an ultraviolet-transparent material, such as fused quartz, isprovided therein for observation purposes. The interiors of the robotarms include a continuous gas passage therethrough so that gas issupplied from an external source through the robot arms to the gasdistribution plate 293. The gas used is dependent upon the operation tobe effected; in epitaxial deposition system the gas will be eitherhydrogen or nitrogen, depending upon the particular operation then beingconducted. Gas can be supplied from any conventional gas container orsource.

The present invention provides three distinct but related advantages.The first advantage is to provide a wafer pick up and delivery apparatusfor use in a high speed, continuous, single wafer processing systemwhich apparatus will not damage the wafer. The second advantage is toprovide every possible means of reducing or eliminating particulatecontaminants to the order of two or three particles per wafer. The thirdadvantage is to provide for a "hot" pick up wherein processed wafers canbe picked up within a few minutes after processing.

A typical operation of the present invention may be summarized asfollows. Robot arms 41 are normally maintained in the home position. Topick up a wafer from station 29, plate assembly 39 rotates until pick uwand assembly 43 faces access slot 35 of the station; the robot arms aremaintained in the home position during rotation. Once the rotationstops, robot arms 41 are extended to pass the pick up wand assemblythrough the access slot and to a cassette for picking up a wafer andtranslating motion is stopped. The wafer is picked up when the flow ofgas is commenced after the robot arms are stationary above the wafer tobe lifted. After pick up, the robot arms are retracted to the homeposition and held in that position while the plate rotates to positionthe pick up wand assembly in allignment with the entrance to reactor 27.The robot arms are extended to position the wafer on the susceptortherein and the flow of gas is stopped resulting in release of the waferand deposit of the wafer on the susceptor. The robot arms are withdrawnto the home position while the wafer is processed. The robot arms areextended back into the reactor to pick up the processed wafer while itis still hot. To lift the wafer, the flow of gas is initiated; after thewafer is picked up, the robot arms retract to the home position. Plateassembly 39 is rotated until the loaded pick up wand assembly ispositioned in front of the access slot to a station. To deposit thewafer within a cassette housed in the station, the robot arms areextended. Terminating the flow of gas will release the wafer upon thecassette. In the final step, the robot arms retract to the home positionto position them ready for a further cycle. It may be noted that theflow of gas is intermittent to minimize turbulence of particulatematter.

We claim:
 1. A wafer transport apparatus having an arm for transportinga wafer from one location to another and a wand assembly supported bythe arm for releasably retaining the wafer in response to an out flow ofgas received through the arm from a source of gas, said wand assemblycomprising in combination:a) a plate having a planar bottom surface,said plate including a longitudinal axis extending forward and rearwardof said plate; b) a central outlet disposed in t bottom surface of saidplate and generally coincident with the longitudinal axis forestablishing an omnidirectional flow of gas across the wafer uponretention of the wafer, said central outlet being oriented essentiallynormal to the bottom surface of said plate; c) a first plurality ofoutlets disposed in the bottom surface of said plate on one side of thelongitudinal axis for establishing a plurality of streams of gas flowtoward the perimeter of the wafer upon retention of the wafer and forchanneling the gas flow from said central outlet intermediate theplurality of streams of gas flow from said first plurality of outlets,said first plurality of outlets including at least one outlet orientedrearwardly and laterally from the longitudinal axis and at least oneoutlet oriented forwardly and laterally from the longitudinal axis; d) asecond plurality of outlets disposed in the bottom surface of said plateon the other side of the longitudinal axis for establishing a pluralityof streams of gas flow toward the perimeter of the wafer upon retentionof the wafer and for channeling the gas flow from said central outletintermediate the plurality of streams of gas flow from said firstplurality of outlets, said second plurality of outlets including atleast one outlet oriented rearwardly and laterally from the longitudinalaxis and at least one outlet oriented forwardly and laterally from thelongitudinal axis; e) means disposed within said plate for channelingthe gas received from the arm through said central outlet, said firstplurality of outlets and said second plurality of outlets; and f) meansdisposed at the rear of said plate for limiting the rearward movement ofa retained wafer.
 2. The apparatus as set forth in claim 1 wherein eachof said first and second plurality of outlets include a greater numberof said outlets oriented rearwardly and laterally of the longitudinalaxis than the number of said outlets oriented forwardly and laterally ofthe longitudinal axis.
 3. The apparatus as set forth in claim 1including a further outlet disposed along the longitudinal axis forestablishing a steam of gas flow rearwardly along the longitudinal axis.4. The apparatus as set forth in claim 1 including a further outletdisposed along the longitudinal axis for establishing a steam of gasflow rearwardly along the longitudinal axis wherein said central outletis disposed along the longitudinal axis.
 5. The apparatus as set forthin claim 2 including a further outlet disposed along the longitudinalaxis for establishing a stream of gas flow rearwardly along thelongitudinal axis.
 6. The apparatus as set forth in claim 1 including aplurality of interconnecting passageways disposed in said wand assemblyfor interconnecting each of said central outlet and said first andsecond plurality of outlets with the outflow of gas from the arm.
 7. Theapparatus as set forth in claim 3 wherein the positional pattern definedby said first and second plurality of outlets and said central outletdefine a truncated bisected isosceles triangle having an imaginary apexat the rear of said plate.
 8. A wafer transport apparatus operating inaccordance with Bernoulli's principle, said apparatus comprising incombination:a) an arm for transporting a wafer from one location toanother, said arm including means for conveying a flow of gas from asource of gas; b) a wand assembly supported upon said arm for releasablyretaining the wafer to be transported and for receiving a flow of gasfrom said arm; c) a plate attached to said wand assembly for defining abottom planar surface of said wand assembly, said plate including alongitudinal axis extending forwardly and rearwardly of said plate; d) afirst plurality of outlets disposed in the bottom surface of said plateon one side of the longitudinal axis for exhausting the gas received bysaid wand assembly and for establishing a plurality of streams of gasflow toward the perimeter of the wafer upon retention of the wafer, saidfirst plurality of outlets including at least one outlet orientedrearwardly and laterally from the longitudinal axis and at least oneoutlet oriented forwardly and laterally from the longitudinal axis; e) asecond plurality of outlets disposed in the bottom surface of said plateon another side of the longitudinal axis for exhausting the gas receivedby said wand assembly and for establishing a plurality of streams of gasflow toward the perimeter of the wafer upon retention of the wafer, saidsecond plurality of outlets including at least one outlet orientedrearwardly and laterally from the longitudinal axis and at least oneoutlet oriented forwardly and laterally from the longitudinal axis; f) acentral outlet disposed in the bottom surface of said plate andgenerally coincident with the longitudinal axis for exhausting the gasreceived by said wand assembly and for establishing a flow of gasomni-laterally and intermediate the plurality of streams of gas flowemanating from said first and second plurality of outlets upon retentionof the wafer; and g) means disposed rearwardly of said central outletfor limiting rearward movement of a retained wafer.
 9. The apparatus asset forth in claim 8 wherein each of said first and second plurality ofoutlets include a greater number of said outlets oriented rearwardly andlaterally of the longitudinal axis than the number of said outletsoriented forwardly and laterally of the longitudinal axis.
 10. Theapparatus as set forth in claim 8 including a further outlet disposedalong the longitudinal axis for augmenting a stream of gas flowrearwardly and essentially along the longitudinal axis.
 11. Theapparatus as set forth in claim 10 wherein each of said first and secondplurality of outlets include a greater number of said outlets orientedrearwardly and laterally of the longitudinal axis than the number ofsaid outlets oriented forwardly and laterally of the longitudinal axis.12. The apparatus as set forth in claim 8 including a plurality ofinterconnecting passageways disposed in said wand assembly forinterconnecting each of said central outlet and said first and secondplurality of outlets with the outflow of gas from said arm.
 13. Theapparatus as set forth in claim 11 wherein the positional patterndefined by said first and second plurality of outlets and said centraloutlet define a truncated bisected isosceles triangle having animaginary apex at the rear of said plate.
 14. The apparatus as set forthin claim 8 wherein said limiting means extends from said plate.